Foamed artificial filament



Nov. 19, 1968 .1. c. LEWIS, JR

FOAMED ARTIFICIAL FILAMENT Filed Aug. 24, 1965 FIG."2

FIG."4

FlGrl INVENTOR JOHN C. LEWIS, Jr.

MORGAN, FINNEGAN, DURHAM 8 PINE ATTORNEYS United States Patent 3,411,979 FOAMED ARTIFICIAL FILAMENT John C. Lewis, Jr., Middlebury, Vt., assignor to Polymers,-

Inc., Middlebury, Vt., a corporation of Vermont Filed Aug. 24, 1965, Ser. No. 482,100 4 Claims. (Cl. 161-178) This invention relates to foamed artificial filaments. More specifically, it relates to synthetic brush fibres having physical properties of the same order of magnitude as natural vegetable fibres for subsequent useage in corn broom, Whisks, brushes, and the like.

Synthetic filaments are presently produced do not possess many of the important characteristic properties heretofore known for the natural vegetable fibres. Natural vegetable fibre structures (cellulosic in nature) are formed by a process of biological growth which consequently results in a cellular structure; i.e., wood. The cross-sections of these fibres are largely irregular, oftentimes having oval, polygonal, lobular or asteroid shapes. These cross-sections are rarely uniform along the length of the fibre axis, thusly they provide for different amounts of material to be distributed across and along the longitudinal length of the fibre in substantially periodic repetition. Also natural vegetable fibres possess non-uniformity in their stiffness profile and for a given longitudinal portion along their length comprising both increasing and decreasing stiffness zones adjacent to one another in a repetitious manner.

Unlike synthetic fibres, natural vegetable fibres cannot be oriented (orientation being the process whereby the macromolecules of a thermoplastic polymer are aligned in a generally parallel relationship, thus resulting in a molecular arrangement parallel to the length of the fibre axis). The natural vegetable fibres, however, are comprised of aggregates of crystalline and non-crystalline material exhibiting a preferential axial orientation along the length of the fibre with some random orientation of the aggregates in the fibre cross-section. It is this natural or biological alignment of crystalline and noncrystalline aggregates of material along the fibre axis which imparts to the fibre a non-uniform stiffness profile. It has been discovered that by controlling the manner in which synthetic filaments are oriented, properties representative of those for natural vegetable fibres can be obtained.

It is, therefore, a primary object of this invention to provide an artificial filament of polymers and co-polymers of propylene having a cellular nature whereby resiliency and high stiffness qualities are obtained making it practically useful as a substitute for natural vegetable fibres.

Another object of this invention is to provide an artificial filament of polymers and c0polymers of propylene having a cellular nature where specific gravities are less than those heretofore known for thermoplastic brush fibres.

Another object of this invention is to provide an artificial filament of polymers and co-polymers of propylene having a cellular nature whereby superior recovery characteristics are obtained.

Yet another object of this invention is to provide an artificial filament of polymers and co-polymers of propylene having a cellular nature whereby excellent fatigue resistance is maintained throughout its length.

Still another object of this invention is to provide an artificial filament of polymers and co-polymers of propylene having a cellular nature whereby the cross-sectional shape resembles that for a natural vegetable fibre.

Still a further object of this invention is to provide an artificial filament of polymers and co-polymers of propylene having a cellular nature whereby non-uniform 3,41 1,979 Patented Nov. 19, 1968 cross-sectional areas of cellular material are integrally present along its entire length in a repetitious manner.

Other objects and advantages of the invention are apparent and can be realized from the complete description thereof which follows.

The preferred filaments of this invention are made from isotactic polypropylene. By isotactic polypropylene is meant polypropylene comprising crystallizable isotactic molecules and up to 15% of amorphous, non crystallizable macromolecules. Polymers of the aforedescribed type are described in US. Patent No. 3,106,442. However, isotactic propylene co-polymers wherein propylene monomer is in a major amount, e.g. polyallomers which are propylene-ethylene co-polymers, also can be utilized as the thermoplastic material from which the novel filaments of this invention are so formed.

The foregoing objects may be realized by (1) forming an unoriented foamed filament comprising an irregular cross-sectional shape, e.g. bilobal, (2) passing unoriented filament into an orienting zone and effecting partial orientation to the filament whereby repetitious oriented portions along the filament length, said oriented portions comprising cross-sectional areas of cellular material less than the original unoriented portion and (3) introducing the resulting filament into an annealing zone whereby any and/ or all processing strains are relieved.

In the drawings:

FIGURE 1 is a longitudinal view of the preferred filament of this invention.

FIGURE 2 is a cross-section of the filament in this invention taken through II-II of FIGURE 1.

FIGURE 3 is a cross-section of the filament in this invention taken through III-III of FIGURE 1.

FIGURE 4 is a cross-sectional view of another form of a filament in this invention.

In order to fully understand the novel nature of the filament in this invention it becomes necessary to describe each of its component parts; it being appreciated that each of these components are contributory in the overall end result. First the filament as stated in the foregoing objects must possess an internal cellular struc ture whereby the resulting specific gravity of the filament approaches or is of the same order of magnitude as natural vegetable fibres, this being somewhat less than 0.80. All commercial thermoplastic polymers, at present, possess specific gravities in the range from 0.905 to 1.70, where polypropylene has a low specific gravity of 0.905 and polyvinylidene chloride a high specific gravity of 1.70. In order to overcome the objectionable specific gravity of even 0.905 for polypropylene filaments it becomes necessary to alter the existing polymeric compounds in some manner; e.g. creating gas voids or vacuols within the polymeric mass, similar to cellulosic fibres. This can be achieved through foaming the polypropylene during the heat melting extrusion process and further controlling the foaming by subsequent cooling in order to develop specific gravities for the resulting filaments in the range from 0.50 to 0.905. Specific reference to the foaming process will be made in the examples hereinafter cited.

Secondly, the cross-sectional shape is important in that it contributes to the stiffness profile of the filament. A non-uniform or irregularly shaped cross-section, e.g. bilobular, has an inherent stiffness which is dependent largely upon the smallest dimension in the cross-section. Unlike circular cross-sections, where the average stiffness is approximately the same when measured from any tangential point, non-uniform cross-sections do not have an average stiffness equal to the average of the stiffnesses taken at the smaller and larger dimensions, but however, have a stiffness which is much less than the average, and whose magnitude is more of the order of the stiffness of the smaller dimension. The filament in this invention makes use of this whereby a large cross-sectional mass of material may be shaped irregularly, but the resulting stiffness for that filament is less than the stiffness which could result if the same crosssectional mass were made circular.

Thirdly, and most important, the filament of this invention must have located along its length (1) repeated and adjacent areas of comparatively large, unoriented mass and comparatively small oriented mass, which, together, combine to impart to the novel filament rigidity, bulking, recovery, fatigue resistance and stiffness. More particularly, the repetitious and adjacent areas of mass are so formed that the large areas of material are in the unoriented state. By providing oriented portions along the foamed filaments length, said portions having smaller cross-sectional areas of material, there is formed zones of highly oriented crystalline aggregates of mass whereby these oriented zones resemble those in the aforedescribed natural fibre. And while having present unoriented portions along the filaments length, there is provided areas having rondomly distributed or nonoriented aggregates of crystalline and noncrystalline material.

It will be understood that the foregoing general description and the following detail description as well are exemplary and explanatory of the invention but not restrictive thereof.

Referring now in detail to the invention, FIGURE 1 illustrates the preferred filament in accordance with the invention, although such form is given by way of example only, and other forms may be employed. As shown in FIGURE 1 the foamed filament 1 has present along its length portions of material 2 and 3 having two discrete cross-sectional areas, the larger portion 2 being in the unoriented state, and the smaller portion 3, being in the oriented state. All the unoriented portions are adjacent, :and in repetious fashion, to the oriented portions along the filaments length. Each specific portion 2 and 3, are of uniform cross-section throughout their length and comprise unit length as designated by L and L in FIGURE 1. The cross-sectional shape of filament 1 is bilobular, each unoriented lobe 5 and oriented lobe 6 radiating from a common central core C and C as shown in FIGURES 2 and 3. When the unoriented portion 2 along the filament is oriented to a given amount there is no change in the cross-sectional shape as shown in the cross-section in FIGURE 3 as taken along IIIIII of the filament in FIGURE 1. The lobes 5 in FIGURE 2 radiate from the central portion C at about equal angles from each other as designated by the letter a. When subjecting the unoriented portion 2 to orientation there is no change in the angular arrangement of the lobes 6 in FIGURE 3. The foamed filament has present throughout its length vacuols 4 as shown in the cross-section of FIGURES 2 and 3. These vacuols or cell-line structures provide the cellular nature in the filament, and are present in both the unoriented and oriented portions. The vacuols in the unoriented portion became elongated due to the orientation process. However, there is no alteration during orientation in the amount of the vacuols present per unit length, and there is encountered no change in the specific gravity in each of the unoriented and oriented portions.

In forming the novel filament as shown in FIGURE 1, it is necessary to use a thermoplastic composition containing a sufficient quantity of foaming agent, e.g. 1 to by weight, whereby, through the decomposition of the foaming agent into gaseous products while under the influence of heat, there is produced within the thermoplastic mass vacuols of discrete size and order. By subsequent quenching, after the foamed hot-melt is extruded through an orifice of predetermined shape, the size of the gas void (vacuol) which is trapped within the filament mass can be controlled, thus by having a uniform distribution of foaming agent within the thermoplastic composition during the extrusion, and by carefully controlling the decomposition temperature, a homogeneous cell structure results.

A preferred foaming agent used in practicing this invention is 1,1-azobisformamide (Kempore R-125) wherein the 1,1'-azobisformamide decomposes by the influence of heat (temperatures in excess of 190 C.) to gaseous decomposition products. Other foaming agents may be utilized when practicing this invention as long as its composition allows decomposition with the elimination of CO N and/ or the like.

The quenched filament after extrusion is wanmed prior to orientation by employing any suitable means for heating. After having been warmed (temperatures in the order of -110 C.) the filament is then introduced into an orienting zone whereby the filament is continuously stretched, while Warm, to a given amount which allows only partial orientation to take place. The resulting filament has both unoriented and oriented portions along its length in a repetitious manner. It must be realized that in order to obtain continuously the repetitious portions of both unoriented and oriented material along the filament length two important procedures must be followed: (1) low orientation ratios, e.g. 2l, 3-1, 3.6-1, must be used and (2) the filament cannot be heated above C. prior to orientation. If either of the procedures are altered beyond these limits, a completely oriented filament will result. The so treated filament is then annealed at high temperatures, e.g. 300 F. for period of time. e.g. 1 hour.

The filaments according to this invention may possess diameters (diameter here is the smaller dimension taken through the cross-sectional shape) which range from 0.015 to 0.150 inch for the unoriented portion and fiom 0.0005 to 0.075 inch for the oriental portion. The preferred range for the unoriented portion is from 0.020 to 0.050 inch and for the oriented portion, from 0.010 to 0.040 inch. Also, the filaments according to this invention may possess unit lengths for the unoriented portion ranging from 5 to inch, while the unit length for the oriented portion may range from A; to 2 inches. The aggregate length of the oriented portions generally comprise at least 40% but not exceeding 80% of the total length of the filament and preferably at least 50% and not exceeding 75% of the total length.

Following the general techniques described hereinbefore, the following are specific Working examples of the preparation of foamed polypropylene filaments having the aforementioned objects in accordance with this invention.

EXAMPLE NO. 1

A mixture of 1 part isotactic polypropylene (Avisun polypropylene 1014; molecular weight 110,000; crystalline melting point of C.; and isotacticity of 98%) and 1 part isotactic polypropylene containing a foaming agent (Avisun polypropylene 1014F-20; molecular weight of 110,000; crystalline melting point of 145 C.; and isotacticity of 98%) are blended with 2% tampico color composite and introduced into the hopper on a 1-inch extruder (20-1 The heats are set at the following temperatures: Die-265 C.; cylinder No. 1-199 C.; and cylinder No. 2176 C. The extruder was fitted with a ver tically disposed die consisting of two holes drilled along a common axis in order to effect a common core, e.g. bilobular. The extrudiate is quenched using a Waterbath maintained at 50 C. and removed at a linear rate of 65 feet per minute. The filament is then passed over a heated roll Whose temperature is maintained at 95 C. This results in warming the filament to 95 C. before introduction into the orientation zone. The filament is then drawn through the orientation zone at a speed of feet per minute (orientation ratio being 3-1) and subsequently wound upon a paddle. By maintaining an orientation ratio less than 4-1 it is possible to efiect a discontinuous orientation in a continuous manner of the foamed fila- (e) Natural palmetto. (f) Natural palmyra. (g) Natural broom corn.

(2) Shape of fibres refers to the shape of the cross-secment which results in a nonuniformdistribution of un' 5 oriented and oriented areas of material along the length t1onalare-a' of the filament Live steam is introduced in the orienting (3) Duflenslon measuredat the Smallest dlameter of one during this rocess but as the artiall oriented fila the fibre; m the case of the bllobular types measuremant :nent f p th p y h d h is taken as the diameter of the lobe; in the case of the oval emerges mm c e Zone 1t Q e types, measurement is taken as the smaller dimension of cold water in order to terminate further orientation. The 10 the oval ultin wound filament on the addle is then introduced F g p (4) Orientation only refers to the portion of filament into an annealing oven for 1 hour at a temperature of which is machine oriented at zzztizzizazztifaatas: 3.25.1522: 3t Selle e using a the unoriented lobes is 0053 inch and 0 0278 inch for samples having a 11/2111] ch-1ength and an r-edmgs corthe Oriented lobes The ()riented portions comprise p 1D rected to a S-gram weight in the second poistion on the proximately 50% of the total length of the filament. if??? f gl were t i t: m f 2 f d e ers o e average s ness in e oriente por- EXAMPLE 2 tions of the synthetic filaments.

This example is prepared in the same manner as Exam- (B) Refers to the average stiffness in the unoriented porple 1 excepting that the orientation ratio is 3.61. The tion of the synthetic filaments; also, the individual naturesulting filament produced in accordance with the exam ral fibre sizes. ple has a density of 0.780 and an average stiffness of (C) Refers to the average stiifness found for the synthetic 24.25. The diameter of the unoriented lobes is 0.0437 filaments when tested using single filament strands proinch :and 0.0223 inch for the oriented lobes. The oriented duced in accordance with the invention. portions comprise approximately 60% of the total length (D) Refers to the average stiffness found for the natural of the filament. l fibres when tested using all of the diameters present.

TABLE I Percent Stifiness (5) Type of fibre (1) Shape of fibre (2) Specific Dimension, (3) orientation gravity inch in drawn (A) (B) (C) (D) zone (4) Synthetic (a) Bilobular 0. 780 8:82;? Synthetic (b) d0 0.180 382%}, Synthetic (c) .do 0.780 8 82;; Synthetic (a) .-do 0.780 8 8%, 0. 0230 0.0165 Palmetto (e) Oval 381?, 0. 0137 0. 0231 Palmyra (I) Bilobular 0. 800 3.8%; Broom Com (g) Oval EXAMPLE NO. 3 From Table I it is seen that it is possible by the present invention to produce synthetic fibres which compare favor- A filament is prepared in the same manner as Example ably with natural fibres. For example, palmyra fibre whose 2 except in place of isotactic polypropylene there is emcross-sectional shape is bilobular and specific gravity less ployed 1 part of crystalline polyallomer (Eastman than 0.80 has an average dry stillness of 24.00. The 5021A) having a melt flow of 2.5 dg. per minute and a synthetic filament a of Table I has a bilobular cross-secspecific gravity of 9.095 and one part of the aforedetional shape, specific gravity of 0.78 and a dry stifiness scribed polyallomer containing 5% foaming agent (1,1'- of 24.25. azobisfor-mamide). Referring now to the physical prop- The filaments of this invention may be used to prepare erties obtained by the novel filament in this invention, it lmprovtid P W as! com floor Scrub can be demonstrated that any desired stiffness profile can brushes Wlsks, Pollshmg brushes and the be obtained by controlling the size of the foamed It shrould be understood that the foamed unoriented/ thetic filament in conjunction with the unit length of the qnented filaments this mvennon may contam conven' oriented repetitious portions. Table I which follows, is i a1 filament aqdmves such a colorants extenders Plashomers and modifiers as practice dictates. concerned with stiffness measurements for the filaments I claim: according to this invention, and compares their stiffness L A foamed Synthetic brush filament having a homog to the sufiness found for natural Vegetable fibresenous cell structure formed from a long chain linear stable In Table I: thermoplastic polymer selected from the group consisting 1 types f fib of propylene polymers and co-polymers comprising: a

cross-section of at least two lobular projections extend- (a) Foamed or ented/unor ented polypropylene. ing from each other at about equal angles from a common Foamed polypropylenecenter portion, said filament having repeated unoriented Foamed 0l'1 I1tBd/uI10f1 eI1ted P yp pylene. and oriented portions adjacent to one another through its (d) Foamed onented/unonented polypropylene. entire length, said unoriented portions having a larger cross-sectional area than the oriented portions, the aggregate lengths of the oriented portions being at least 40% but not more than 80% of the total length of the filament, said filament having a specific gravity not exceeding 0.080, whereby varying amounts of stiffness and recovery are im parted to the filament along its length.

2. A foamed synthetic brush filament according to claim 1 wherein the thermoplastic polymer is isotactic propylene.

3. A foamed synthetic brush filament according to claim 1 wherein the orientation ratio of the oriented portion is in the range of 2-1 to 4-1.

4. A bilobular foamed synthetic brush filament according to claim 1.

References Cited UNITED STATES PATENTS Reis 161179 X Cramton 15-159 Trotin 161-479 X Adams 16l---179 Bottomley 161-178 ROBERT F. BURNETT, Primary Examiner.

J. D. FOSTER, Assistant Examiner. 

1. A FOAMED SYNTHETIC BRUSH FILAMENT HAVING A HOMOGENOUS CELL STRUCTURE FORMED FROM A LONG CHAIN LINEAR STABLE THERMOPLASTIC POLYMER SELECTED FROM THE GROUP CONSISTING OF PROPYLENE POLYMERS AND CO-POLYMERS COMPRISING: A CROSS-SECTION OF AT LEAST TWO LOBULAR PROJECTIONSD EXTENDING FROM EACH OTHER AT ABOUT EQUAL ANGLES FROM A COMMON CENTER PORTION, SAID FILAMENT HAVING REPEATED UNORIENTED AND ORIENTED PORTIONS ADJACENT TO ONE ANOTHER THROUGH ITS ENTIRE LENGH, SAID UNORIENTED PORTIONS HAVING A LARGER CROSS-SECTIONAL AREA THAN THE ORIENTED PORTIONS, THE AGGREGATE LENGTHS OF THE ORIENTED PORTIONS BEING AT LEAST 40% BUT NOT MORE THAN 80% OF THE TOTAL LENGTH OF THE FILAMENT, SAID FILAMENT HAVING A SPECIFIC GRAVITY NOT EXCEEDING 0.080, WHEREBY VARYING AMOUNTS OF STIFFNESS AND RECOVERY ARE IMPARTED TO THE FILAMENT ALONG ITS LENGTH. 